As shown in FIG. 7, a scroll compressor in prior art comprises a stationary scroll 11, an orbiting scroll 10, and an isolating member 12. The inner side of the stationary scroll 11 has a predetermined number of spiral scroll plates. The stationary scroll 11 has a through discharge port 111 at the center thereof. The orbiting scroll 10 has a predetermined number of projecting spiral scroll plates to be assembled with the stationary scroll 11. The scroll plates form a plurality of compression rooms between the two scrolls. The orbiting scroll 10 is driven (by an eccentric shaft connected to a motor) to orbit the stationary scroll 11 but not to rotate on its axis such that working fluid is led into the compression rooms, compressed from low pressure through middle pressure to high pressure, and discharged at high-pressure state via the discharge port 111 of the stationary scroll 11. The isolating member 12 is fixed in a shell 1 of the scroll compressor and partitions the shell 1 into a high-pressure chamber 2 and a low-pressure chamber 3. A through hole 122 is disposed at the center of the isolating member 12 to connect the two chambers 2 and 3. A predetermined number of back pressure rooms 123 near the low-pressure chamber 3 are installed at positions at the same distance from the axis of the through hole 122. The stationary scroll 11 is located in the low-pressure chamber 3. The projecting edge of the discharge port 111 at the back of the stationary scroll 11 forms a tubular neck 112. The neck 112 is lagged in the through hole 122 of the isolating member 12 and can make a little motion along the axis of the through hole 112. A sealing ring 125 of back pressure mechanism and a resilient member 126 are installed in the neck 112. The sealing ring 125 presses on the resilient member 126 to build back pressure. An anti-leakage member 124 is installed between the outer surface of the sealing ring 125 and the inner surface of the neck 112 to prevent high-pressure working fluid of the discharge port 111 from leaking into the low-pressure chamber 3. A predetermined number of pressing members 13 are respectively accommodated in each back pressure room 123 to be lapped on the back 113 of the stationary scroll 11. An anti-leakage member 114 is installed between each pressing member 13 and each back pressure room 123. When the stationary scroll 11 and the orbiting scroll 10 are engaged, compressed working fluid generated therein is led into the back pressure rooms 123 to drive each pressing member to stick to the back 113 of the stationary scroll 11 such that the stationary scroll 11 sticks tightly to the orbiting scroll 10. Therefore, when the orbiting scroll orbits the stationary scroll 11, the two scrolls are tightly joined in the axial direction to prevent compressed working fluid in each compression room from leaking out.
As shown in FIGS. 6a and 6b, the pressing member 13 is a bolt of cylindrical shape 13b or of cylindrical cup shape 13a. In the prior art, to maintain compression stability and balance of the isolating member 12, th pressing member 13 must be evenly arranged at least every 120 degrees. Three back pressure rooms require three pressing members (also called axial submission bolts) and three corresponding anti-leakage members. If there are more back pressure rooms, more pressing members and anti-leakage members are needed such that the assembly process becomes more complex and the products cost thereof becomes higher. As shown in FIG. 9, a pressing member of annular groove shape 14a or annular shape 146 (both shown in FIGS. 8a and 8b) have been proposed in the prior art for use with a corresponding back pressure room of annular shape. However, an annular projecting edge 115 must be installed on the back of the stationary scroll 11 to stick to each pressing member 13 or 14a, 14b. Process complexity and production cost are thus increased. As shown in FIG. 10, a guide hole 116 of the tubular neck 112 of the stationary scroll 11 and a connection hole 121 disposed in the isolating member 12 have been proposed such that the compression room and the back pressure room 123 are connected. However, process complexity is increased. Also, inequality of pressure in the compression room may result in imbalance of the pressing member such that noise easily arises, abrasion of components increases, and thus lifetime is reduced.